1. Field of the Invention
The present invention relates to a communicating apparatus wherein a number of terminal equipment are connected to a network, and to be further detailed, it relates to a circuit controlling terminal equipment identifiers identifying terminal equipment.
2. Description of the Prior Art
The apparatus performing communication processing according to the HDLC (High-level Data Link Control)-type data link layer controlling procedure has been known. FIG. 1 shows a configuration of an in-house network shown in the CCITT Recommendation I.430, and a subscriber line 41 such as a telephone line controls an in-house bus 42, and a controlling apparatus 43 terminating the subscriber line is connected thereto, and terminal equipments TE0, TE1 . . . TEn such as a telephone and a facsimile are connected to the in-house bus 42. Numerals 44 in the figure designate terminating resistors.
In the above-mentioned Recommendation, one telephone number corresponds to one controlling apparatus 43, and discrimination of the terminal equipments TE0, TE1 . . . TEn is made using subaddresses called terminal equipment identifiers TEI. For this reason, it is prescribed that the terminal equipment stores the TEI value thereof, and compares the TEI value of a received number with the TEI value of itself, and takes in the received signal when the both values match with each other.
FIG. 2 shows a terminal equipment identifier controlling circuit for performing this operation. Numeral 5a designates an n-bit register storing the TEI values of itself. Taking these values as X.sub.0. . . X.sub.n-2, X.sub.n-1, these bits are given to exclusive NOR gates 5.sub.0. . . 5.sub.n-2, 5.sub.n-1. On the other hand, the TEI values of the received n bits Y.sub.0. . . Y.sub.n-2, Y.sub.n-1 becomes another input of the above-mentioned exclusive NOR gates 5.sub.0. . . 5.sub.n-2, 5.sub.n-1, and the output thereof is inputted to an AND gate 5b of n input.
Numeral 5c designates a comparator constituted with the NOR gates 5.sub.0, 5.sub.n-2, 5.sub.n-1 and the AND gate 5bb. And, as obvious from the configuration of this comparator 5c, when the receieved TEI value and the TEI value of itself stored in the register 5a match with each other, a match output is obtained at the AND gate 5b, and thereby the terminal equipment judges that the received signal is for itself, and takes in this received signal transmitted with TEI values, and in the case of mismatch, it neglects that signal.
Then, in accordance with the CCITT Recommendation Q.921, one terminal equipment is allowed to have one or more TEI values. Accordingly, in the case where the equipment has a plurality of TEI values, a plurality of registers 5a and comparators 5c are required respectively, and thereby a problem exists that the amount of hardware is increased and the time required for comparison is extended.
Also, the TEI value to be assigned to one terminal equipment is unknown in designing and manufacturing it, and therefore another problem exists that no rational design can be performed.
In addition, apart from this, the network side is required to control the TEI values assigned to all terminal equipment.